1. Field of the Invention
The present invention relates to a method of and an apparatus for measuring the thickness of a magnetic layer of a magnetic recording medium or the like.
2. Description of the Related Art
There has heretofore been employed a process of measuring the thickness of a magnetic layer contained in a magnetic recording medium such as a magnetic tape (first measuring process) with a micrometer.
According to the first measuring process, the overall thickness of the magnetic recording medium is measured by the micrometer. Then, a magnetic layer, a back coat layer, etc. are removed from the magnetic recording medium using a suitable solvent, and the thickness of the remaining portion of the magnetic recording medium is measured by the micrometer. The measured thickness of the remaining portion is subtracted from the measured overall thickness of the magnetic recording medium to determine the thickness of the magnetic layer.
The recent trend of magnetic recording mediums is for their layers to be greatly reduced in thickness. According to the first measuring process, it is difficult to measure the thickness of such thin magnetic layers with sufficient accuracy. The first measuring process is also disadvantageous in that it takes a long period of time to measure the thickness of a magnetic layer because a destructive approach is employed to remove the magnetic layer, the back coat layer, etc. with the solvent.
Another process of measuring the thickness of a magnetic layer (second measuring process) is a non-destructive process using a radiation such as .beta.-rays, .gamma.-rays, X-rays, etc.
There are several types of the second measuring process, and they include a transmissive measuring process, a fluorescent X-ray measuring process, and a back scatter measuring process. These measuring processes determine the thickness of a magnetic layer based on an interaction between the radiation and the constituent substance of the magnetic layer.
Specifically, the mass per unit area of the constituent substance of the magnetic layer is measured from the interaction between the radiation and the constituent substance, and the mass is divided by the density of the constituent substance to determine the thickness of the magnetic layer.
The second measuring process needs to obtain a certain large sample for measuring the mass per unit area of the constituent substance of the magnetic layer. Therefore, the determined thickness of the magnetic layer represents an average thickness. It is thus difficult to achieve a sufficient resolution (spatial resolution) commensurate with an increase in the magnetic recording density in recent years.